1. Field of the Invention
The present invention relates to a magnetic resonance imaging (MRI) apparatus with a gradient coil for generating a gradient magnetic field upon energizing the gradient coil.
2. Description of the Related Art
In a general MRI apparatus, a cylindrical bobbin is disposed between a space through which a subject enters and a gradient coil. In terms of the bobbin, the subject is prevented from directly contacting with the gradient coil (for example, see JP-A-8-196518).
However, in a recent MRI apparatus, current flowing into the gradient coil tends to increase. As a result, a radiant heat that is generated from the gradient coil upon energizing the gradient coil increases. For this reason, a problem arises in that the bobbin is heated by the radiant heat so that a temperature of the bobbin becomes high, and thus the subject may feel uncomfortable.
Particularly, in the recent MIR apparatus, it is demanded that an opening through which the subject enters is enlarged in order to improve an amenity of the subject. For realizing the demand, a spacing distance between the gradient coil and the bobbin necessarily decreases, and thus the radiant heat of the gradient coil makes easily the temperature of the bobbin high.
Further, in the MRI apparatus, an iron shim for controlling uniformity of static magnetic field may be disposed between a static magnetic field magnet and the gradient coil. When the iron shim is heated by the radiant heat of the gradient coil, a problem arises in that an influence of the iron shim with respect to the static magnetic field varies, and thus the uniformity of a static magnetic field may vary.